Carbon dioxide removal from natural gas to meet specifications can in principle be achieved through the use of different sweetening technologies. Examples of applicable technology options for carbon dioxide removal are chemical and physical absorption, membrane separation, pressure-swing adsorption (PSA), and cryogenic/low-temperature distillation.
In a known low-temperature distillation process, methane is withdrawn from the top of a distillation column and carbon dioxide and heavy hydrocarbons are withdrawn from the bottom. Heat exchangers are used in the distillation process to cool the feed stream from gas to liquid phase or reboil liquid in the column to generate vapor phase for mass transfer between the phases based on difference in volatilities.
Recently, it has been proposed that a cryogenic/low temperature distillation system can be used to remove carbon dioxide from offshore natural gas fields. These gas fields may contain as little as 30% hydrocarbons and 70% carbon dioxide. The offshore system will have to reduce the carbon dioxide level dramatically to produce a usable product. Such offshore processing systems face significant difficulties due to the offshore environment.
For example, the overall weight and footprint of such systems are of a significant concern in offshore operations. Designers endeavor to identify ways that the overall weight and surface area can be reduced without adversely affecting the efficiency of the system. Furthermore, it is desirable to maintain a system height that is as low as possible.
Therefore, there is a need for effective and efficient systems for offshore processing of high carbon dioxide natural gas.